This invention relates to a grinding machine which grinds a flat surface of a circular wafer-shaped work or the like/using a grinding stone, in which it is especially intended that the work can be ground with a good degree of flatness and its surface roughness is improved.
In the prior art, when a flat surface of a circular wafer-shaped work or the like is ground as a grinding surface, the creep feed grinding as shown in FIG. 3(a) or the work rotation grinding as shown in (b) in the same figure has been carried out.
By the way, in the creep feed grinding, in a state in which a grinding surface A of a work W is subjected to face-contact with an end face of a cup type grinding stone 10, have the work W reciprocate toward the shaft center side of the grinding stone while have the grinding stone 10 rotate around its shaft center. Using such reciprocal movement of the work W, it is made that the cup type grinding stone 10 grinds the grinding surface A of the work W. In addition, in the work rotation grinding, the grinding surface A of the work W is subjected to face-contact with the end face of the cup type grinding stone 10 by a certain length L, and in a state in which the contact length L is fixed, have the work W and the grinding stone 10 rotate around each of the shaft centers, respectively. Using such rotation of the work W and the grinding stone 10, it is made that the grinding stone 10 grinds the grinding surface A of the work W.
However, in the conventional creep feed grinding as described above, since the reciprocal movement of the work W is used to make the grinding stone 10 to grind the grinding surface A of the work W, the contact length L between the grinding stone and the work becomes shortest when the grinding stone is located at the outer peripheral portion of the work, and on the contrary, the contact length L becomes longest when the grinding stone passes through the central portion of the work, so that not only the grinding load which is inflicted to a grinding stone shaft (not shown) through the grinding stone changes depending on periodic change of the contact length, but also since the grinding stone 10 always contacts with the work W in the state of face-contact in the creep feed grinding, the grinding load inflicted to the grinding stone shaft as described above is relatively large and which bends and deforms the grinding stone shaft, therefore it is difficult to grind the grinding surface of the work with a good degree of flatness.
On the other hand, also in the conventional work rotation grinding, in the same manner as the creep feed grinding, since the grinding stone 10 always contacts with the work W in a state of face-contact, the grinding load inflicted to the grinding shaft through the grinding stone is relatively large and which bends and deforms the grinding stone shaft, so that it is difficult to grind the grinding surface of the work with a good degree of flatness.
Moreover, in the work rotation grinding, the contact length L between the grinding stone 10 and the work W is fixed in a state of being relatively long, and a grinding amount by one grinding stone particle of the grinding stone is large, so that especially when a grinding stone of fine grinding stone particles is used, grinding burning of the work takes place due to the clogging of the grinding stone. Therefore, the grinding particle size of the grinding stone has certain restriction with respect to the diameter of the grinding surface, and only a grinding stone of grinding stone particles having a large diameter not less than the restriction can be used, and it is impossible to improve the surface roughness of the grinding surface.